A rhabdomyosarcoma in an inbred strain of rat is being used to study the response of a solid transplantable tumor after irradiation by heavy ion beams produced at the Bevalac at Lawrence Berkeley Laboratory. Tumor volume response, survival at several positions in the "spread-out" depth dose (Bragg) curve are being measured. The oxygen effect will also be studied in the "spread-out" region of the depth-dose curve. In addition, the kinetics of tumor cells will be measured after irradiation. These results will be compared with similar studies using 220 kV X-rays and the helium ion beam at the 184 inch cyclotron. In addition, the overall response of the tumor is being studied by the development of a computer model which includes the more important mechanisms affecting the growth and regression of the tumor.